{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T10:03:32Z","timestamp":1784714612405,"version":"3.55.0"},"reference-count":57,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T00:00:00Z","timestamp":1784678400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Background\/Objectives: Exogenous ketone supplementation has been proposed to enhance endurance performance by altering substrate metabolism and sparing muscle glycogen. Prolonged carbohydrate restriction may upregulate ketolytic capacity and could therefore modulate the response to exogenous ketone ingestion. This study investigated the impact of increasing circulating ketone bodies through exogenous ketone supplementation on endurance performance in athletes chronically adapted to a ketogenic diet. Methods: Participants (n = 9 recreationally active males, with \u22651 year of ketogenic adherence) visited the lab four times. The first visit determined their V.O2max. The second visit accustomed them to test procedures. In a counterbalanced design, visits three and four tested the consumption of a 60 g carbohydrate beverage (CHO), or a beverage comprising 60 g carbohydrate and 0.5 g\/kg 1,3-butanediol (CHO + BD). This was followed by a 60 min set-intensity exercise bout, followed by a 16.1 km time trial. Results: \u03b2HB significantly increased in the CHO + BD group (rest: 0.72 \u00b1 0.33 mmol\/L; post-exercise: 1.69 \u00b1 0.30 mmol\/L) compared to CHO (rest: 0.80 \u00b1 0.53; post-exercise: 0.55 \u00b1 0.30) (p &lt; 0.001). There was no significant difference in time trial performance between groups (1606 \u00b1 138 s; 1620 \u00b1 134 s; p &gt; 0.05). During set intensity exercise, there was no significant main effect of supplementation on lactate concentration, substrate oxidation, oxygen consumption at a fixed workload, RPE or heart rate (p &gt; 0.05). However, glucose was significantly lower at minutes 40 and 60 of set intensity exercise in CHO + BD compared to CHO. Conclusions: No significant effect of 1,3-butanediol ingestion on endurance performance was detected in this sample of nine chronically ketogenic male athletes. \u03b2HB significantly increased from resting levels; however, time trial performance did not differ between conditions. Given the small sample and limited statistical power, these preliminary findings indicate no detectable ergogenic effect under the present conditions rather than evidence of no effect, and larger studies are warranted.<\/jats:p>","DOI":"10.3390\/nu18142388","type":"journal-article","created":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T09:20:39Z","timestamp":1784712039000},"page":"2388","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Acute 1,3-Butanediol Co-Ingestion with Carbohydrate Does Not Improve Endurance Performance in Chronically Ketogenic Male Athletes"],"prefix":"10.3390","volume":"18","author":[{"given":"Matthew","family":"Carpenter","sequence":"first","affiliation":[{"name":"School of Life Sciences, Pharmacy and Chemistry, Kingston University London, London KT1 1LQ, UK"},{"name":"School of Sport and Public Health, University of Northampton, Northampton NN1 5PH, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7938-2803","authenticated-orcid":false,"given":"James","family":"Brouner","sequence":"additional","affiliation":[{"name":"School of Life Sciences, Pharmacy and Chemistry, Kingston University London, London KT1 1LQ, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9465-1693","authenticated-orcid":false,"given":"Owen","family":"Spendiff","sequence":"additional","affiliation":[{"name":"School of Life Sciences, Pharmacy and Chemistry, Kingston University London, London KT1 1LQ, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,7,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"327","DOI":"10.1301\/nr.2003.oct.327-341","article-title":"Ketones: Metabolism\u2019s ugly duckling","volume":"61","author":"VanItallie","year":"2003","journal-title":"Nutr. 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